Current demands for high-density data storage and high performance and reliability require tape handling systems which store as much tape as possible on a single supply reel in a cartridge. Such demands for increased density, performance and reliability require cartridges which are as simple and rugged as possible.
Certain conventional tape drives, referring to FIG. 1, comprise a modular data cartridge 1 having a supply reel 2. The cartridge 1 is inserted into the tape drive through a front bezel 3, then the tape 4 is pulled out of the cartridge 1 and fed past a magnetic read/write head 5 and wound onto a take up reel 6, which is not removable from the tape drive. Upon rewinding the tape 4 back onto the supply reel 2, the end of the tape 4 is captured in the cartridge 1, at which time the cartridge 1 can be removed from the tape drive.
When the cartridge 1 is outside of the tape drive, the supply reel 2 must be locked to prevent it from rotating and causing the tape 4 to unravel if the tape 4 is subject to harsh environmental conditions such as shocks and vibrations. In conventional tape drive/cartridge designs, this reel locking function is typically accomplished by providing gear teeth at the outside diameter of the supply reel and a lever or levers with a corresponding gear tooth profile which are normally engaged with the supply reel gear teeth by means of a spring force. When the cartridge is inserted into the tape drive, mechanisms inside the tape drive disengage the lever(s) from the supply reel gear teeth and allow the supply reel to rotate.
These conventional external reel locks are disadvantageous because they are complex and require a large number of parts, which makes them unreliable and costly. Furthermore, because they have a number of separate mechanisms which must operate separately when the cartridge is loaded into the tape drive, they slow down the operation of the tape drive.
Referring again to FIG. 1, to move the tape 4 from the supply reel 2 to the take up reel 6, the supply reel 2 is normally rotated by a motor (not shown). For the supply reel 2 to rotate, it must therefore engage the motor, and an adequate engagement force must be applied between the motor and the supply reel 2 to maintain their engagement. The supply reel 2 should also easily disengage from the motor when the cartridge 1 is to be removed from the tape drive. In conventional tape drive/cartridge designs, a magnetic coupling scheme is typically employed which utilizes the principle that a holding force exists when a magnetically soft material, such as steel, is in contact with a permanent magnet. In such a magnetic coupling design, a steel plate is attached to the supply reel of the cartridge and a ring-shaped, axially magnetized permanent magnet is attached to the motor coupling. When the supply reel is brought into contact with the motor coupling, the steel plate comes into contact with the magnet on the motor coupling, thereby coupling the motor and the supply reel.
The holding force of the magnetic coupling depends on the strength of the magnetic material. Additionally, the force between the steel plate and the permanent magnet is inversely proportional to the distance between them. The force has a maximum value when the steel and the magnet are at zero distance from each other; that is, when they are in contact with each other. The amount of force decreases as the distance between the steel and magnet increases. Thus, depending on the strength of the magnet, the force will become essentially zero at a certain distance between the steel plate and the magnet. Disadvantageously, the condition of zero force between the steel plate and the magnet may not be attainable in the short distance desired for coupling engagement/disengagement travel; that is, if there is limited space available between the steel plate and the magnet. Thus, in applications in which compactness is at a premium, complete disengagement (zero force) may not be achievable with magnetic coupling.
Another disadvantage to the magnetic coupling scheme is that because the force between the steel and the magnet is at a maximum when they are coupled, an undesirable impact force to the cartridge may be created when the cartridge is disengaged from the motor coupling. Also, when the motor coupling and the supply reel are being engaged, the magnet may "grab" the supply reel; that is, pull the reel towards it with a jerk, undesirably impacting the reel.
Furthermore, the magnetic properties of the permanent magnet vary with temperature. Since the motor coupling is close to the motor and attached to the motor shaft, it may reach the same temperature as the motor, thus undesirably altering the magnitude of the coupling force. Still further, the height of the magnet undesirably increases the overall coupling height. Moreover, the need to adhesively bond the magnet to the motor coupling and to bond the steel plate to the supply reel add additional assembly operations to the manufacture of the tape drive and the cartridge.
There exists a need for a tape cartridge with uncomplicated and reliable reel lock and motor/reel coupling engagement systems. There also exists a need for a reel lock and a coupling mechanism which are both activated by a single motion of the cartridge or drive motor, thus reducing the complexity of and the time required for the cartridge loading operation.